Breaking stress of neutron star crust

TL;DR

This paper investigates the breaking stress of neutron star crust through molecular dynamics simulations, modeling its dependence on temperature and timescale, with implications for neutron star phenomena like glitches and gravitational waves.

Contribution

It introduces a detailed molecular dynamics approach combined with the Zhurkov model to estimate neutron star crust breaking stress over astrophysically relevant timescales.

Findings

Breaking stress depends strongly on temperature at long timescales.

Matter can break at very small stress over years for certain coupling parameters.

An alternative timescale-independent model provides an upper limit estimate.

Abstract

The breaking stress (the maximum of the stress-strain curve) of neutron star crust is important for neutron star physics including pulsar glitches, emission of gravitational waves from static mountains, and flares from star quakes. We perform many molecular dynamic simulations of the breaking stress at different coupling parameters (inverse temperatures) and strain rates. We describe our results with the Zhurkov model of strength. We apply this model to estimate the breaking stress for timescales ~1 s - 1 year, which are most important for applications, but much longer than can be directly simulated. At these timescales the breaking stress depends strongly on the temperature. For coupling parameter <200, matter breaks at very small stress, if it is applied for a few years. This viscoelastic creep can limit the lifetime of mountains on neutron stars. We also suggest an alternative model of timescale-independent breaking stress, which can be used to estimate an upper limit on the breaking stress.